Copper‐Catalyzed Oxidative Transformation of Aryl Propargylic Azides to Aryl Propiolonitriles

A concise copper(I)‐catalyzed oxidative transformation of aryl propargyl azides to aryl propiolonitriles has been developed. Aryl propiolonitrile derivatives can be obtained in moderate to good yields by this strategy. An oxidative Schmidt rearrangement is involved in this transformation.     

Ruthenium‐Catalyzed β‐Alkylation of Secondary Alcohols with Primary Alcohols

Cyclopentadienyl (Cp), hydrotris(pyrazolyl)borato (Tp), and bipyridine ruthenium complexes were found to be active catalysts for the β‐alkylation of secondary alcohols with primary alcohols. Mechanistic aspects of the Cp and Tp complexes‐catalyzed reactions were investigated; the crucial hydrido complexes were identified. Carbonyl complexes resulting from aldehyde decarbonylation were formed in some cases, and surprisingly, they were also found to be active for the catalytic processes.     

Copper‐Catalyzed Trifluoromethylation of Acrylamides Coupled with Indole Dearomatization: Access to Trifluoromethyl‐Substituted Spiro[indole‐3,3′‐pyrrolidine] Derivatives

A copper‐catalyzed cascade reaction involving trifluoromethylation of acrylamides coupled with ring closure and indole dearomatization is reported. This facile transformation was highly regioselective and proceeded under mild conditions, allowing efficient access to trifluoromethyl‐substituted spiro[indole‐3,3′‐pyrrolidine] derivatives, which are of increasing interest to the pharmaceutical industry.

     

A Stereoselective Access to Cyclic cis‐1,2‐Amino Alcohols from trans‐1,2‐Azido Alcohol Precursors

A unique one‐pot synthesis of cyclic cis‐1,2‐amino alcohols from trans‐1,2‐azido alcohol precursors was developed. The key step is highlighted by the stereoselective reduction of the cyclic α‐alkoxy imines, which could be prepared from the corresponding azides by ruthenium catalysis under photolytic conditions. Remarkably, this unprecedented reaction pathway offers a stereodivergent access to structurally diverse cyclic 1,2‐amino alcohols.

     

Copper‐Catalyzed Activation of Dioxygen: Oxidative Cyclization of 2‐Arylindoles

A series of unusual six‐ring‐fused heterocycles containing indole and quinoline skeletons was successfully synthesized by a copper‐catalyzed reaction from 2‐arylated indoles. Two new bonds were regioselectively formed from C H and C H coupling. ¹⁸O‐Labelled experiments revealed that the dioxygen is not only the oxidant but also the reactant.     

Copper‐Catalyzed Aryltrifluoromethylation of N‐Phenylcinnamamides: Access to Trifluoromethylated 3,4‐Dihydroquinolin‐2(1 H)‐ones

A method for copper‐catalyzed aryltrifluoromethylation of N‐phenylcinnamamides is reported. This method provides a straightforward route to a variety of CF₃‐containing 3,4‐dihydroquinolin‐2(1 H)‐ones with excellent regioselectivity and diastereoselectivity.

     

Copper‐Catalyzed C‐Arylation and Denitrogenation of Tetrazoles: Domino Synthesis of 1,3‐Diaminoisoquinoline Derivatives

An unexpected copper‐catalyzed sequential C‐arylation and denitrogenation of tetrazoles leading to 1,3‐diaminoisoquinoline derivatives has been developed, and the corresponding 1,3‐diaminoisoquinoline derivatives were obtained in moderate to good yields. The method provides a novel strategy for the synthesis of isoquinoline derivatives containing various functional groups.     

The Copper‐Catalyzed Oxidative N‐Acylation of Sulfoximines

An oxidative cross‐coupling reaction between aldehydes and sulfoximines involving dual C H/N H functionalization has been developed. This reaction process is facilitated by a simple copper catalyst (1 mol% loading) and tert‐butyl hydroperoxide (TBHP) as the oxidant and proceeds under mild reaction conditions to afford a series of valuable N‐acylated sulfoximine derivatives in excellent yields.     

An Efficient Copper‐Catalyzed Homocoupling of Terminal Alkynes to Give Symmetrical 1,4‐Disubstituted 1,3‐Diynes

A facile and efficient pathway for the copper iodide and ligand N,N,N′,N′‐tetramethylethane‐1,2‐diamine promoted homocoupling reaction of terminal alkynes under ambient temperature and air as an oxidant was reported. The alkynes, including aromatic alkynes and aliphatic alkynes, could afford the symmetrical 1,4‐disubstituted 1,3‐diynes in good to excellent yields.     

Copper‐Catalyzed N‐Alkylation of Sulfonamides with Benzylic Alcohols: Catalysis and Mechanistic Studies

The N‐alkylation of sulfonamides with alcohols is efficiently performed in the presence of easily available copper catalysts via hydrogen borrowing methodology. Applying a copper acetate/potassium carbonate system the reaction of sulfonamides and alcohols gave the corresponding secondary amines in excellent yield. In situ HR‐MS analysis indicated that bissulfonylated amines are formed under air atmosphere, which act as self‐stabilizing ligands for the catalytic system. UV‐visible measurements suggest the interaction between the copper centre and the bissulfonylated amine. Reactions of benzyl alcohol‐d₇ with p‐toluenesulfonamide, N‐benzyl‐p‐toluenesulfonamide or N‐benzylidenetoluenesulfonamide revealed that the reaction proceeds via a transfer hydrogenation mechanism and the whole process is micro‐reversible. Competitive reactions of benzyl alcohol and benzyl alcohol‐d₇ with p‐toluenesulfonamide revealed a kinetic isotope effect (kH/kD) of 3.287 (0.192) for the dehydrogenation of benzyl alcohol and 0.611 (0.033) for the hydrogenation of the N‐benzylidene‐p‐toluenesulfonamide intermediate, which suggests that dehydrogenation of the alcohol is the rate‐determining step.     

Copper‐Catalyzed Diastereoselective Synthesis of Trifluoromethylated Tetrahydrofurans

The copper‐catalyzed intramolecular diastereoselective trifluoromethylcycloetherification of homoallylic alcohols with Togni’s reagent as trifluoromethylating reagent was realized under mild conditions. Various trifluoromethylated tetrahydrofurans were synthesized in moderate to good yields. Moreover, a wide range of common functional groups was tolerated.

     

Copper‐Catalyzed Selective Oxidative Acylation of Secondary Anilines with Ethyl Glyoxalate: Domino Synthesis of Indoline‐2,3‐diones

A novel, easy and useful copper‐catalyzed selective acylation of secondary anilines with ethyl glyoxalate has been developed, and the corresponding indoline‐2,3‐dione derivatives were prepared. The procedure comprises the sequential intermolecular copper‐catalyzed selective oxidative ortho‐site aromatic acylation of the NH group in secondary anilines and intramolecular nucleophilic attack of the NH group to the ester. The inexpensive, easy and efficient method should provide a new strategy for synthesis of dicarbonyl compounds.     

Copper‐Catalyzed Efficient Multicomponent Reaction: Synthesis of Benzoxazoline‐Amidine Derivatives

We have developed an efficient copper‐catalyzed method for the synthesis of the benzoxazoline‐amidine derivatives. The protocol uses inexpensive copper(I) iodide as the catalyst, and furnished the expected product in good to excellent yields by a three‐component reaction of sulfonyl azides, terminal alkynes and Schiffs’ bases in terahydrofuran (THF) at room temperature for 8 h in the presence of triethylamine. This novel synthetic protocol is selective, efficient and general. A plausible mechanism for this process is proposed.     

Room Temperature Aerobic Copper–Catalysed Selective Oxidation of Primary Alcohols to Aldehydes

A novel and very mild method for the oxidation of primary alcohols to aldehydes with excellent conversions has been developed. The reaction is carried out under air at room temperature and is catalysed using a [copper(II)‐(N ligand)_n] complex with TEMPO and a base as co‐catalysts. In this paper, the performance of a series of N‐containing ligands, as well as different copper(II) salt precursors in different solvents are reported. Best results are obtained in acetonitrile/water as solvent using a copper(II) catalyst generated in situ from a Cu(II) salt with weak or non‐coordinating anions and bipyridine ligands with electron‐donating substituents. A reaction mechanism is postulated which resembles that of galactose oxidase, and in which TEMPO seems to be involved as a hydrogen acceptor.     

Lewis Acid‐Catalyzed Oxidative Allylation: A New Approach for the Synthesis of Homoallylic Alcohols and Amines Directly from Alcohols

A new approach for the synthesis of homoallylic alcohols and amines directly from alcohols via one‐pot sequential oxidation–Barbier reaction and oxidation–condensation–Barbier reactions, respectively, is reported. The protocol involves the one‐pot ferric chloride‐catalyzed oxidation of alcohols to the corresponding aldehydes with chloramine‐T followed by indium‐mediated Barbier allylation with allyl bromide to afford homoallylic alcohols in 70–90% overall yields. The ferric chloride‐catalyzed condensation of aldehydes and oxidation by‐product p‐toluenesulfonamide followed by indium‐mediated Barbier‐type allylation of the resulting aldimines with allyl bromide affords homoallylic amines in 60–80% overall yields in the same reaction vessel. The present work demonstrates a new one‐pot approach toward homoallylic alcohol and amine synthesis directly from alcohols.     

Ligand Controlled Highly Selective Copper‐Catalyzed Borylcuprations of Allenes with Bis(pinacolato)diboron

Copper‐catalyzed highly selective borylcuprations of allenes with bis(pinacolato)diboron produce two different types of alkenylboranes by applying a ligand effect. In the presence of tris(para‐methoxyphenyl)phosphine [P(C₆H₄OMe‐p)₃], the reaction of aryl‐1,2‐dienes affords 2‐alken‐2‐yl boronates as the only product with exclusive Z‐geometry; the regioselectivity is switched to afford the 1‐alken‐2‐yl boronates as the major products when the bidentate phosphine 2,2′‐bis(diphenylphosphino)biphenyl is used as the ligand.     

Copper‐Catalyzed Three‐Component Synthesis of 2‐Iminodihydrocoumarins and 2‐Iminocoumarins

An efficient synthesis of N‐sulfonyl‐substituted 2‐imino‐3,4‐dihydrocoumarins and 2‐iminocoumarins via a copper‐catalyzed multicomponent reaction of sulfonyl azides with terminal alkynes and β‐(ortho‐hydroxyphenyl)‐α,β‐unsaturated ketones or ortho‐hydroxyphenylpropiolates has been developed. The cascade process involves trapping the keteimine by a nucleophilic addition and an intramolecular Michael addition. This methodology could well be extended to the concise synthesis of the polysubstituted piperidine scaffold.     

Ruthenium Catalyzed Selective Regio‐and‐Mono‐Allylation of Cyclic 1,3‐Diketones Using Allyl Alcohols as Substrates

The new ruthenium‐sulfonate catalyst Ru(Cp*)(η³‐C₃H₅) (p‐CH₃C₆H₄SO₃)₂, (Cp*=pentamethylcyclopentadienyl), rapidly and regioselectively mono‐allylates dimedone to the branched products using substituted allyl alcohols as substrates, without acid, base or other additives, under relatively mild conditions. We consider the ruthenium sulfonate to be a “green” alternative in that it uses allyl alcohols as substrate, (rather than carbonates, acetates, etc.) and therefore does not waste the leaving group. The catalyst induces rapid double allylation of various 1,3‐diketones in high yield using allylic alcohol.     

Copper‐Promoted Coupling of Carbon Dioxide and Propargylic Alcohols: Expansion of Substrate Scope and Trapping of Vinyl Copper Intermediate

We have successfully demonstrated that in the presence of N,N‐diisopropylethylamine, copper iodide could efficiently catalyze the coupling of internal propargylic alcohols with carbon dioxide to afford the corresponding α‐alkylidene cyclic carbonates in moderate to excellent yields. Moreover, we have developed a new and versatile protocol for the chemo‐ and stereoselective synthesis of a wide range of (E)‐α‐iodoalkylidene cyclic carbonates from carbon dioxide, propargylic alcohols and potassium iodide using copper salt as the promoter. The process is proposed to proceed through the trapping of the vinyl copper intermediate by in situ generated triiodide ion as electrophile.